The present invention relates generally to the field of liquid and air separation and in particular to a deaerator apparatus and deaeration system for removing air bubbles from a variety of fluids such as coatings.
There are several basic processes for removing air bubbles by centrifugal force. Each process has its drawbacks and none of these is used to make totally air free coating today.
The hydrocyclone spins fluid inside a tube based on the inlet velocity. Hydrocylcones are limited in the viscosity they can treat and cannot remove all air as the fluid exits the separation chamber under pressure allowing bubbles to effervesce at normal atmospheric pressure.
A rotating tank has similar problems. In addition, it is also expensive and limited in the RPM that can safely be achieved.
Another process is a stationary tank with vanes spinning inside. However, thermal or heat buildup is a problem in these systems.
One process does exist that is capable of producing a totally air free coating. This process uses rotating disks inside a vacuum chamber to make a very thin layer. The layer is thin enough so the bubbles rise to the surface and break. Unfortunately, these machines are very expensive because the vacuum chamber has a heavy walled construction to resist implosion. These machines are also difficult to control and keep clean.
Specific apparatuses or systems for removing air bubbles are discussed in more detail below.
U.S. Pat. No. 4,435,193 to Gullichsen et al. discloses a centrifugal pump comprising a housing, an inlet channel at one end of the housing, a fluid outlet at the periphery of the housing, a rotor having axially extending blades, a gas exit chamber separated below the separation chamber by a partition wall, a gas discharge in the gas exit chamber, and openings in the partition wall for communication between the chambers. A suspension is rotated within the pump so that a gas bubble is created at a central part of the pump, and gas is discharged from the gas bubble at a gas discharge pressure. The gas discharge leads to a vacuum pump.
The discharge flow rate of the fluid is controlled by a valve and flow meter in the fluid outlet. A dP instrument is connected between the fluid outlet and a liquid container from which the fluid is introduced into the inlet. A dP controller is connected to the fluid inlet and gas discharge to measure the differential pressure between the suspension inlet and the gas discharge.
U.S. Pat. No. 3,546,854 to Muller discloses a non-rotative centrifugal separator comprising a cylindrical casing, an inlet pipe at one end of the casing, an outlet pipe and a drain pipe at the opposite end, and a baffle assembly comprising vanes mounted on a mounting rim in the shape of a disc. Centrifugal force separates a gaseous fluid into a gaseous stream in the center and an annular envelope of the liquid particles. The gaseous stream exits the outlet while the fluid exits through the drain.
U.S. Pat. No. 3,597,904 to Jakobsson et al. discloses a liquid gas separation apparatus comprising a pump housing, an inlet leading to the housing, a gas discharge pipe contained within the inlet along a central axis of the pump housing, a vacuum source connected to the gas discharge pipe, a pump rotor driven by a shaft for rotating shovels so that the fluid along the walls passes through an outlet at the periphery of the housing.
U.S. Pat. No. 4,136,018 to Clark et al. discloses a vortex separator comprising a cylindrical chamber, an inlet at a first end, coaxial with and surrounding a lightweight rejects pipe, a shaft imparting rotational motion to an impeller at a second opposite end, a perforate wall at the second end, an accepts chamber leading to an accepts pipe, and a heavy rejects outlet in a side wall adjacent the first wall. The impeller defines an annular passage.
U.S. Pat. No. 4,382,804 to Mellor discloses a fluid particle separator comprising a cylindrical housing containing a separator comprising a disk of substantially the same diameter as the internal wall of the housing, leaving a small radial clearance. The disc is formed with a plurality of vanes. A baffle plate is provided behind the separator. A fluid inlet is provided at one end of the housing and a fluid outlet is provided at the opposite end.
U.S. Pat. No. 4,416,672 to Underwood discloses an apparatus for removing gas from mud comprising a chamber having an inlet at one end and mud and gas outlets at the opposite end. A shaft is located centrally along the axis of the chamber and is attached to vanes and two discs spaced apart. As the shaft discs and vanes rotate, a centrifugal force is imparted to the mud separating the gas from the mud. The mud exists through a circumference or peripheral outlet while the gas exits through a plurality of gas outlets.
U.S. Pat. No. 4,955,992 to Goodale et al, discloses a liquid degassing system comprising a liquid reservoir having an inlet for receiving a liquid, an outlet for expelling degassed liquid and a vacuum source controllably connected through a valve to draw gas out of the liquid. A baffle prevents air bubbles from passing to the outlet while allowing the fluid to pass through to the outlet. A valve in the liquid inlet may interrupt flow to the reservoir while a vacuum is applied. A second valve in an outlet conduit may interrupt flow from the reservoir when a vacuum is applied.
U.S. Pat. No. 5,324,166 to Elonen et al. discloses a centrifugal pump comprising a housing with a liquid flow inlet, an impeller with pumping vanes and a central gas passage, and a gas outlet connected to an external vacuum pump. Gas is separated by the impeller and pumping vanes and is collected in the center of the housing where it is withdrawn through the central gas passage of the impeller to the gas outlet.
U.S. Pat. No. 4,976,586 to Richter et al. discloses a pump system comprising a housing with an inlet and an outlet, an impeller having a hub and blades, a hollow tubular body with vanes mounted on a shaft which rotates and forces pulp to the impeller. Gas collected at the impeller is withdrawn through a passage in the shaft of the tubular body via an exterior vacuum pump.
U.S. Pat. No. 5,622,621 to Kramer discloses a fluid separator comprising a cylindrical rotating bowl, an inlet at one end of the drum, circumferentially spaced vanes near the inlet and outlet parts circumferentially spaced about the inlet leading to a gas manifold. Water accumulates at the periphery of the bowl while lighter density gas is forced into the outlet parts. The water moves onto a disk pump compartment via axial passages formed in the periphery of the walls of the bowl.
A centrifugal air compressor having a hub with radially arranged blades is known from U.S. Pat. No. 2,611,241 to Schulz.
Pressure monitoring control of valves is known from U.S. Pat. No. 5,190,515 to Eaton et al. which discloses a system for sensing and controlling the liquid level in a centrifuge bowl comprising a pressure sensor at the outlet of the bowl connected to a controller and valve of the inlet. Gas is withdrawn from the housing via a vacuum source.
U.S. Pat. No. 1,993,944 to Peebles teaches a centrifugal pump in which the pressure inside the pump is monitored to control a valve at the outlet.
U.S. Pat. No. 5,800,579 to Billingsley et al., discloses a pressure control apparatus for a cyclone separator comprising a differential pressure transducer for measuring the pressure within the chamber of the cyclone separator. A pressure sensor is located in the separation chamber and a microprocessor controller ascertains pressure differences between a preset valve and a pressure in the separation chamber. A variable flow control valve is associated with a discharge opening of the chamber and increases air flow in response to increased pressure in the separation chamber sensed by the controller.
There is a need for deaerators that can produce a totally air free coating while having a low heat buildup. Additionally, there is a need in the art for such apparatuses to have a structure which can easily be disassembled for cleaning. Finally, in light of current technologies which use expensive vacuum systems to achieve totally air free coatings, there is a need for an inexpensive solution for producing totally air free coatings. In particular, a deaeration system is needed in which the high cost of a large vacuum chamber and the resulting high cost of creating a vacuum are overcome. There is also a need for differential pressure monitoring for affecting incoming and outgoing fluids and process controls that assure the delivery of air free fluids regardless of process disruptions such as excessive incoming air or temporary loss of vacuum.